Stirling cycle engine with two wave cam means, two piston banks and driveshaft



May 28, 1968 D. A. KELLY 3,385,051

STIRLING CYCLE ENGINE WITH TWO WAVE CAM MEANS TWO PISTON BAN AFT KS AND DRIVESH Filed Feb. 10, 1967 3 Sheets-Sheet 1 F l 2 A 55 INVENTOR.

May 28, 1968 D. A. KELLY 3,385,051

STIRLING CYCLE ENGINE WITH TWO WAVE CAM MEANS, TWO I PISTON BANKS AND DRIVESHAFT 3 Sheets-Sheet 2 Filed Feb. 10, 1967 INVENTOR D. A. KELLY 3,385,051 STIRLING CYCLE ENGINE WITH TWO WAVE CAM MEANS TWO May 28, 1968 PISTON BANKS AND DRIVESHAFT 5 Sheets-Sheet 3 Filed Feb. 10, 1967 INVENTOR. dud/0% United States Patent Oflice 3,385,051 STIRLTNG CYCLE ENGINE WITH TWO WAVE CAM MEANS, TWO PISTON BANKS AND DRIVESHAFT Donald A. Kelly, 58--06 69th Place, Maspeth, N.Y. 11378 Filed Feb. 10, 1967, Ser. No. 615,095 7 Claims. (Cl. 60-24) ABSTRACT OF THE DISCLOSURE A Stirling cycle engine having a drive shaft and a plurality of power pistons arranged axially about said drive shaft, and a power wave cam co-axially mounted on the drive shaft; a plurality of displacer pistons arranged axially about said drive shaft, and a displacer wave cam co-axially mounted on the driveshaft.

The classic Stirling closed cycle is basically an externally heated engine in which a constant volume of gas is alternately heated and cooled to produce the half-power stroke and half-pull stroke on the power piston. Various types of Stirling cycle engines are known, such as the conventional dual-coaxial reciprocating engine now in use, sideby-side piston types and L types. The currently used dualcoaxial piston engine is pressurized and operates at good efficiencies, but due to its configuration is hampered by an excessive number of rods and linkages. This complex linkage assembly is a drawback to the simple ganging of multiple cylinders to achieve efficient, high power-tovolume/ weight Stirling engines.

The present novel design allows for the compact ganging of co-axial displacer and power pistons, axially arranged around two, twin-wave cams mounted on a common drive shaft. The design attempts to circumvent the complex linkage required by the current co-axial engine, by the application of two wave cams on a drive shaft, which by their configuration provide for the phase relationship between the two piston sets. The wave cam provides for the displacement of the piston groups and by placing the earns 45 degrees out of phase, the required half-stroke keying of the cycle is achieved.

The 45 degree phase angle is correct only for a twin wave cam with eight displacer and power pistons, as shown. The phase angle places the pair of displacer and power pistons in the proper half-stroke Stirling differential relationship. It should be noted that the displacer pistons receive energy for reciprocation from their wave cam, While the power pistons transmit thrust to their wave cam to produce the torque at the common drive shaft, and this functioning is analogous to the compressor and power stages of the standard gas turbine. The present Stirling engine design has a distinct advantage over an equivalent gas turbine in that it is a closed cycle engine with its theoretical upper power output limited only by the capability of material steel, filaments, etc. to contain high pressures.

The twin wave cams provide for the complete piston excursion within a 180 degree, one-half revolution of the drive shaft. The helix angle of the twin wave cam is about 40 degrees for optimum revolution of the drive shaft compared to friction level. The power pistons must readily revolve the power wave cam with a reasonable coeflicient of friction between the roller bearings and the cam track.

Unlike the previously disclosed side-by-side multiple piston/cam en ine where the alternating displacer and power pistons are arranged axially around one Wave cam, this design has all the power pistons arranged axially around the power wave cam while the displacer pistons are co-axially in-line with a corresponding power piston,

3,385,951 Patented May 28, 1958 and these displacer pistons are also arranged axially around the displacer wave cam.

An advantage of this arrangement is that the power pulses are more uniformly distributed over the periphery of the cam, rather than by four half-stroke power pulses typical for the previously disclosed side-by-side piston/ cam design. By utilizing eight power pistons and therefore eight sequential half-stroke pulses, the cam is more uniformly loaded and transmits a smooth power flow.

In this arrangement the displacer piston strokes need not be the same as that of the power pistons since each group has its own wave cam and therefore their own displacement stroke. If the two piston groups are in-line as shown in FIG. 2, the displacer cam will inherently be smaller, since the displacer piston must be sealed off with a sealing plate and track which must occupy more radial space as indicated.

It is desirable that the displacer cam stroke be equal to or larger than that of the power cam, to gain advantageous volumetric expansion. Another way to approach this volumetric proportion is to vary the relative bore diameters of the displacer and power pistons.

Due to each bore group being in its own cylinder block section, it would appear feasible to utilize different bore diameters to the advantage of having both piston groups nearly in line.

Accordingly and in consonance with the foregoing, it is a general object of the present invention to provide a simplified Stirling cycle engine, while retaining all the characteristic efliciency of the cycle.

Another object of the invention resides in the achievement of a multiple piston Stirling engine in a minimum volume module.

A further object of the invention is to provide a relatively simple Stirling cycle engine which efficiently conducts heat to the displacer bore and maintains low ambient temperatures at the cold volume thereof.

Another object of the invention is to achieve maximum operating elliciencies in a Stirling engine through the adoption of new and improved thermal saturation techniques.

A further object of the present invention reside in the provision of an engine of this type to operate with a minimum of fluid lubrication and at low friction levels.

A final general object of the described invention is to provide an engine of the described character which will be simple in structure, economical to manufacture and efficient in use.

Other objects and advantages of the described multiple piston, two wave cam Stirling cycle engine will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice of the invention, the same being realized and attained by means of the structure defined and pointed out in the appended claims.

The accompanying drawings referred to herein and constituting a part hereof, illustrate the invention, and together with the description, serve to explain the principles of the invention.

FIGURE 1 is a front elevational cross-sectional view through the displacer bores of the engine.

FIGURE 2 is a side elevational cross-sectional view of the engine.

FIGURE 3 is a front elevational cross-sectional view through the power bores of the engine.

FIGURE 4 is a phase diagram of the relative positions of the displacer and power pistons and their mode of motion.

FIGURE 5 is an exploded view illustrating the working parts of the engine and their inter-relationship.

The present preferred embodiment of the invention as illustrated in the accompanying drawings will now be described, twin wave power cam 1, a key element thereof being clearly shown in FIGURE 5. As shown therein said power cam comprises identical wave portions A and B and is attached to the drive shaft 2 to thereby transform the reciprocating thrusts of the power pistons 3 into rotary motion, which in turn is imparted to the drive shaft.

The power pistons, generally designated herein by numeral 3 and individually as P1, P2, P3, P4, P5, P6, P7, P8, slide within the power bores 4 and thereby transmit motion to cam track 5 of the power wave cam 1, through roller bearings 6, pins 7 being provided to secure said hearings to the sides of the power pistons, respectively, as shown.

The drive shaft 2 revolves on and is supported by thrust roller bearings 8 which are mounted in piston housing portions 9, 10 and 11, said housing being substantially identical in cross-section, such split arrsngcment permitting expedient assembly and disassembly of the engine. Said housing portions are mutually secured by tensile bolts 12 and nuts 13, and sealed by gaskets 14, being provided for both sealing and insulation purposes.

The displaccr pistons, generally designated by numeral 15 and individually as D1, D2, D3, D4, D5, D6, D7, D8, as reciprocated by the cam track 17, of the displacer wave cam 16, through roller bearings 15, pins 19 being provided to secure said bearings to yoke members 20, the displacer pistons 15, being slidably received within displaeer bores 21, as shown.

Sealing plate 22, attached to the displacer pistons, provides a seal between said plate and displacer slot 23, the latter being integrally provided in the piston housing portions 10 and 11 as shown. Since the expanding eg., air, must not escape into the cam volume 24, the sealing plates are required to effectively seal each displacer slot 23, with minimum sliding friction.

The displacer pistons are fitted with ball bearings which are journalled by pins 26, within recesses provided within the longitudinal sides of the displacer pistons to thereby reduce piston side play and friction within the displacer cylinder. The displacer pistons have sufiicient wall gap with respect to said bores 21, to thereby allow the working gas to be shuttled back and forth within the displaeer bores.

End flanges 27 position and support pressure seals 28, at each end of the housings and are secured to each end housing portion 9 and 11 by the screws 29. Liquid sealant is preferably used to seal the joint between the end flanges and the housing portions.

Heat cylinders 30, formed of copper or other suitable heat conductive material, conduct heat from an external heat source, at the end of housing portion 11 and displacer bores 21, the heat cylinders being insulated from the housing portions by use of insulation liners 31, the liners further providing a pressure tight seal and allowing for the expansion of the heat cylinders.

Cooling tubing 32 is formed continuously around the housing portion 10, to cool the cold side of the displacer pistons 15 and displacer bore 21. The cooling tubes carry a suitable liquid coolant and are connected to a supply source and pumping means.

Two thrust collars 33 are secured to the drive shaft 2 at each end thereof and contact the inner race of the thrust roller bearings 8, to transmit thrust and to remove end play in the drive shaft.

Regenerator bores 34 and regenerator filaments 35 are located within the displacer pistons 1.5 and provide a means of alternately storing and giving up heat for maintaining heating economy.

The regenerator bores 34 may be sloped to converge at a single port at the cold side of the displacer piston 15. The regenerator bores may be tapered to achieve a convergence at the cold side of the displacer piston, in addition to the previously described sloping of all the bores.

The purpose of the sloping and possible tapering of the bores is to isolate the hot expanding gas flow from the cold bore walls 21, during the portion of the cycle when the displacer piston is moving into the heated gas zone.

The regenerative filament 35 is the material which absorbs and stores the transmitted heat during one halfcycle and gives it up on the reverse llow for preheating the gas for the next heating and expanding half-cycle.

With reference to FIGURE 2, the line saturation filaments 36, as shown, are uniformly dispersed within the hot and cold ends of the displacer bores 21, said filaments being formed of beryllium copper or other suitable heat conductive material. These filaments are uniformly disposed in the heating and cooling bores 21, as shown, the filaments being effective in uniformly heating and cooling bore volumes 21, and being adapted to flex on contact with the reciprocating displacer pistons.

Each of the displacer bores 21 and power bores 4 should be fitted with gas filler valves 37, a pressure gauge 38, a safety plug 39, and a temperature gauge 4%, as shown, thereby providing a monitor for the operating condition of each of the bore portions.

The two filler valves 37 are provided, one at each end of the power pistons within the housing portion 9, since the power pistons seal off the volumes 21 and 4. In operation the under-ring volume 4 of the power piston must be at working pressure to provide the return thrust during the cooling cycle half.

The pressure gauges 38 are preferably located at the power bore since such location will be at substantially mean temperature and working pressure. The temperature gauges 40, as shown, are preferably arranged in proximity to the heat cylinder 3%, to thereby monitor heat flowing to each bore.

Although the preferred embodiment of the multiple pistol/cam Stirling engine has been described, it will be understood that within the purview of this invention various changes may be made in the forms, details, proportions and arrangement of parts, the combination thereof and mode of operation which generally stated consists of an engine capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

What is claimed is:

1. In a reciprocating Stirling cycle engine having multiple pistons and a pressurized gaseous medium, the combination comprising a housing for a plurality of pistons, a drive shaft rotatably mounted within said housing, two wave cam means mounted on said drive shaft for rotation therewith, a plurality of elongate bores within said housing, said bores each having a longitudinal axis and a forward and rearward end and having equal radii with respect to said drive shaft, said longitudinal axes and said drive shaft arranged in para-llism, multiple pairs of power and displacer pistons arranged co-axially, each of said pairs of pistons being slidably received within said elongate bores for alternating phase reciprocation therewithin, said pistons being operatively associated with respective said wave cam means through coacting roller bearings mounted on said pairs of pistons, means for reciprocating said gaseous medium between a heating zone at one end of each displacer piston and a cooling zone at an opposite end of each displace: piston.

2. The combination set forth in claim 1 wherein said two wave cam means are of circular configuration and each cam means includes a cam track disposed peripherally thereof, said cam track including a pair of identical wave portions, said wave portions being degrees apart.

3. The combination set forth in claim 1 including hearing means interposed between the said displacer pistons and the said elongate bores in which said pistons are received.

4. The combination set forth in claim 1 wherein the said displacer pistons are provided with a flat sealing plate 5 connected to one side thereof in sliding association with an elongate fiat surface within one half of said elongate bores within said housing, elongate centered slots within the elongate flat surfaces, yoke means secured to said sealing plate disposed through the elongate centered slots and supporting said roller bearings.

5. The combination set forth in claim 1 including a relatively thin, flexible thermal conductive filament at at least one end of said displacer piston bores.

6. The combination set forth in claim 1, including heat conducting means disposed within said housing at an end of each bore opposite each displacer housing.

7. The combination set forth in claim 1 wherein one of the said piston bores is provided with heat conducting means arranged at one end and mounted in said housing,

thermal filament interposed between said heat conducting means and said displacer piston.

References Cited UNITED STATES PATENTS 1,390,034 9/1921 Howard 123-58 1,828,353 10/1931 Bleser 123-58 X 2,272,925 2/ 1942 Smith 626 2,468,293 4/1949 Du Pre 62-6 2,482,831 9/1949 Arden 123145 2,567,576 9/1951 Palumbo 12358 X 2,712,483 7/1955 Ciaccia 92178 15 MARTIN P. SCHWADRON, Primary Examiner.

CARROLL B. DORITY, ]R., Assistant Examiner. 

